1. Field of Invention
The current invention relates generally to apparatus, systems and methods for communicating. More particularly, the apparatus, systems and methods relate to wireless communication. Specifically, the apparatus, systems and methods provide for improved reception of signals by analysing two or more signals at the same time and dynamically weighting the signals to product a better resulting signal.
2. Description of Related Art
In digital radio communication systems a signal is transmitted from a transmitting antenna to a receiving antenna via a channel, which channel comprises open space generally containing objects such as the earth and its topographic features (mountains, oceans) as well as buildings, vehicles and other man-made obstructions, in addition to atmospheric gases, that is characterized by several parameters and effects. The primary result of propagation through the channel is an expansion of the signal wave-front (energy) in and along multiple directions, including directions other than the nominally desired direction corresponding to a path between the receiver and transmitter.
The use of antennas having directivity (radiation patterns) reduces the propagation (respectively collection) of energy in (respectively, from) undesired directions. However, as is well known, significant energy can reach the receiving antenna after traveling along paths other than the direct path between the transmitter and receiver. Indeed, in some applications the direct path, also referred to as the line-of-sight path, may not exist at all and the received energy is actually carried by a superposition of waves that have been reflected, refracted and generally scattered during propagation.
The multiplicity of propagation paths and resulting effects on the output of the receiving antenna is referred to as “multipath”. The effects of multipath are determined by the linear superposition (addition) of the multiple electromagnetic waves (or more precisely, electromagnetic fields) at the receiver antenna. This superposition can result in partial cancellation of the received field at the antenna and thus a reduction in received signal energy. This is the well-known and familiar fading process.
In addition, when the respective components of the multipath ensemble arrive at the antenna with distinct time delays (that is, having traversed different path lengths and thus having different propagation times), the components combine in a manner that may result in distortion of the signal. This is also a well-known phenomenon known as frequency selective fading, a term that arises from an analysis of the effect of the differential propagation delays of the respective waves (dispersion) in the frequency domain. What is needed is a better why of receiving multipath signals.